This invention relates to: (i) chemical compounds that are generally useful as pharmaceutically active agents, and in particular as ataxia telengiectasia and Rad3-related (ATR) protein kinase inhibitors; (ii) pharmaceutical compositions comprising one or more of these ATR protein kinase inhibitors; (iii) a process for chemical synthesis of the ATR protein kinase inhibitors; and (iv) methods of using the ATR protein kinase inhibitors to treat various biological disorders, including cancer.